Acute HIV infection is accompanied by inflammation and by a profound loss of CD4+ T cells from the gastrointestinal (GI) tract. Systemic inflammation arising from the gut is now thought to be pathogenic in progression of HIV/AIDS. We hypothesize that a shift towards a Th17 response and away from a pro-inflammatory Th1 response in the setting of acute infection will be protective. We have discovered that the transcription factor T-bet controls the Th1/Th17 balance in vivo both as an activator of Th1 differentiation and as a repressor of Th17 differentiation. Hence, in contrast to the protective role of T-bet for most pathogens, T-bet may actually be deleterious for a patient acutely infected with HIV because it enhances a pro-inflammatory Th1 response in the gut. Of note, there are additional reasons to believe that silencing T-bet will be protective in the setting of acute HIV infection. First, T-bet is a repressor of IL-2 in CD4+ and CD8+ T cells, a cytokine which has been shown to correlate with lower viral load in the elite controller population. Second, T-bet-/- CD4 cells are polyfunctional i.e. "multiple cytokine-secreting", a phenotype recently associated with viral control. We suggest that reducing T-bet expression will 1) increase gut protective Th17 cells;2) reduce pro-inflammatory Th1-driven responses such as macrophage activation;3) increase IL-2 production necessary for functional CD8+ cell T responses and 4) increase numbers of polyfunctional T cells. We will use two different mouse models of AIDS to establish the function of T-bet in vivo. The MAIDs model has provided valuable insights into the immune response against retroviruses and will allow us to test the effect of T-bet absence and T-bet overexpression easily. However, its resemblance to human HIV/AIDs is only partial. If our proof-of-principle experiments in the MAIDS model are encouraging, we will move quickly to the more relevant model, a humanized mouse model called BLT, to ask whether 1) T-bet silencing in human cells provides protection against HIV in vivo and 2) T-bet overexpression exacerbates acute HIV infection. Guided by our results in the MAIDS model, human HSCs will be transduced with lentiviral T-bet siRNAs and T-bet cDNAs for adoptive transfer experiments to BLT mice. Hence, the goal of this proposal is to further explore the function and mechanism of action of a transcriptional activator/repressor, isolated in our laboratory, in the immune response to HIV. It is based on strong preliminary data that T-bet controls the development and function of Th1 cells and represses the development of IL-17 and IL-2 producing cells. The emphasis will be on the role of this gene and its products in the setting of acute HIV infection and ultimately in the generation of durable protective immunity to HIV. PUBLIC HEALTH RELEVANCE: Systemic inflammation arising from the gut is now thought to be pathogenic in progression of acute HIV/AIDS. We have discovered that the transcription factor T-bet controls the Th1/Th17 balance in vivo both as an activator of Th1 differentiation and as a repressor of Th17 differentiation- hence, in contrast to the protective role of T-bet for most pathogens, T-bet may actually be deleterious for a patient infected with HIV because it enhances a pro-inflammatory Th1 response in the gut. We will test the hypothesis that blocking T-bet expression will 1) increase gut protective Th17 cells 2) reduce pro-inflammatory Th1-driven responses 3) increase IL-2 production necessary for functional CD8+ cell T responses 4) increase numbers of polyfunctional T cells and 5) will ameliorate acute disease in two different mouse models of AIDS: MAIDS and the BLT humanized mouse model.